Microemulsions are known in the art. They are stable isotropic mixtures of oil, water, and surfactant. Other components, such as salt or a co-surfactant (an alcohol, amine, or other amphiphilic molecule) may also be part of the microemulsion formulation. The oil and water reside in distinct domains separated by an interfacial layer rich in surfactant. Because the domains of oil or water are small, microemulsions appear visually transparent or translucent, and are not birefringent. Unlike emulsions, microemulsions are equilibrium phases and form spontaneously upon contact of the ingredients.
Microemulsions can have a variety of microstructures, depending mainly on composition and temperature. The common structural feature is the presence of a surfactant-rich sheet separating oil-rich and water-rich domains. There are three most common structures. One is the so-called water-in-oil microemulsions, in which water is contained inside distinct domains (droplets) in a continuous oil-rich domain. A second is oil-in-water microemulsions in which oil is contained inside distinct domains in a continuous water-rich domain. The third is bicontinuous microemulsions in which there are sample-spanning intertwined paths of both oil and water, separated from each other by the surfactant-rich film (a sponge-like structure).
In contrast to bulk and solution polymerization, high reaction rates, high conversions and large molecular weights are achieved using either emulsion or microemulsion polymerization of unsaturated hydrocarbons, which are considered to be oils. In both cases the high rates and conversions and large molecular weights are thought to be obtained because the monomer molecules are concentrated in a number of small regions or domains of the microemulsion, which facilitates reaction among themselves. A microemulsion can be distinguished from a conventional emulsion by its optical clarity, low viscosity, small domain size, thermodynamic stability, and spontaneous formation. Microemulsion polymerization has several advantages over traditional emulsion polymerization. First, emulsions are turbid and opaque, while microemulsions are usually transparent or translucent and so are particularly suitable for photochemical reactions. Second, microemulsion polymerization enables preparation of stable, monodisperse microlatexes containing particles smaller than those produced with classical emulsion polymerization processes. Finally, the structural diversity of microemulsions (droplet and bicontinuous) is set by thermodynamics, and rapid polymerization may be able to capture some of the original structure.
Modification of porous substrates by coating them with fluorinated polymers is known in the literature, thus, porous substrates can be coated with water-repellant polymers in order to increase their hydrophobicity. However, such processes normally require expensive and/or environmental-hazardous fluorinated solvents, such as CFCs. Moreover, water-based emulsion polymerization of fluorinated monomers usually yields particles with sizes in the range of 0.1-10 micron, which makes it difficult to give uniform coatings on substrates having submicron pore structures. In addition, such large particle sizes result in coatings that can clog the pores of micron or submicron pore structures, which is detrimental in many applications.
It would be desirable, therefore, to provide polymeric colloidal dispersions of very small particle sizes made from the monomer microemulsions in order to coat porous substrates in which the pores are micropores.